1. Field of the Invention
The invention is directed to a method for printing individual sheets in a printer or a copier, whereby a both-sided printing process on individual sheets ensues.
2. Description of the Related Art
High-performance printers can be operated in what is referred to as duplex mode, which is also called duplex color spot mode. In this operating mode, individual sheets are printed on both sides. When only one print ensues on the one side and two prints with different colors ensue on the other side, then this is called the duplex printing mode with three-fold printing. When respectively two prints ensue on both sides of the individual sheet, then this is called duplex printing mode with four-fold printing.
Various duplex printing systems with ate least two printing units are disclosed by U.S. Pat. No. 4,591,884 A. Another high-performance printer device with two printing units is disclosed by WO 91/13386 A1. It comprises two printing units and turnover channels for turning the individual sheets over. A transfer printing transport path is allocated to each printing unit.
When individual sheets are supplied such in such a high-performance printer device with two printing units that the spacing between two individual sheets is greater than the length of an individual sheet viewed in transport direction, then a safety margin is created between two individual sheets that allows a further individual sheet to be transferred in upon transport of the individual sheets in gaps between two successive individual sheets at intersections of the sheet transport paths. Given this procedure, however, the sheet throughput is relatively low due to the relatively large sheet spacings.
U.S. Pat. No. 5,159,395 discloses a printer device having only a single printing unit wherein spaces are likewise created between two successive sheets of a sheet stream in order to subsequently transfer further individual sheets into the sheet stream.
U.S. Pat. No. 5,337,135 discloses a further printer device with only a single printing unit wherein a first printing operating condition with a first, relatively close printing spacing is provided and a second operating condition with a second, larger sheet spacing [is provided], whereby following sheets are again transferred into an existing sheet stream in the second operating condition.